The invention discloses a method for synthesizing 3, 8-dimethyl-3, 5, 7-octtriene-1, 10-dialdehyde, the method comprises the following steps: taking 2-butene-1, 4-tetraethyl diphosphate and 4, 4-dimethoxy-2-butanone as raw materials, firstly, taking cyclohexane and methylbenzene as solvents, adding a basic catalyst, a water-absorbing drying agent and crown ether, carrying out low-temperature reaction, then dissolving reactants in a mixed solvent of tetrahydrofuran, acetic acid and water, and carrying out a reaction at a high temperature to obtain the 3, 8-dimethyl-3, 5, 7-octtriene-1, 10-dialdehyde. The alkaline catalyst and the water-absorbing drying agent are added into a reaction system, and crown ether is added for catalysis so that the yield of the synthesized beta-carotene key intermediate is obviously increased, the synthesis process of the intermediate is optimized, the synthesis efficiency of the intermediate is improved, and the synthesis process is easy in raw material obtaining, simple in process, convenient to operate and relatively low in cost, and green development is met and industrialization is easy to achieve.